Commercial Architecture February 2018 - 40
U.S. Steel Tower
Danfoss VLT drives
provide more than $1
million in energy savings.
n 1970, the U.S. Steel Corp. built a unique head-
which occupies 40% of the building's space.
quarters that still stands 64 stories above the
"We're moving a lot of water and air up, down,
Pittsburgh skyline. Built to last 100 years, the sky-
and around this building," said Sechler. "Water is sup-
scraper, now known as the U.S. Steel Tower, is archi-
plied by two redundant water mains. In addition,
tecturally unique. It features a distinctive triangular
there are four redundant, 100-hp water pumps in the
footprint using U.S. Steel-developed Cor-Ten steel
building. Each one can serve the entire building, if
to form an external girding system that allows each
needed. There are also two boilers on the sixty-fourth
story to contain an acre of floor space. While ahead
floor and two centrifugal chillers on the sixty-third
of its time in the 1970s, the building fell behind
floor to provide redundant heating and cooling. So
with mechanical equipment that was installed when
there is a lot of pumping needed for domestic-water
kilowatts cost pennies and oil was $3 a barrel. That's
circulation and for the chilled-water loops, all of
why Winthrop Management, Boston (winthroppgh.
which consume a lot of energy."
com), the building's property manager, began a series
The first drive retrofit project was in the year 2000
of retrofits using Danfoss, Baltimore (danfossdrives.
when VLT drives were applied to four 100-hp pump
com), VLT variable-frequency drives to cut energy
motors responsible for the building's domestic water.
costs, resulting in more than $1 million in energy sav-
"The old drives were two-step drives like they
ings and a greener reputation that's attracting tenants.
used in steel mills back in the day," said Jim Rice,
"We have been applying Danfoss VLT drives in
owner of M&R Affiliates, Upper St. Clair, PA, the
various retrofit projects for nearly 15 years," said Gary
Danfoss sales representative who has been working
Sechler, engineering manager for Winthrop Manage-
with Sechler since he has been in charge. "They
ment. "After every retrofit project phase, we've found
weren't true variable-frequency drives. We replaced
the energy savings on pump motors and fans have
them with four Danfoss VLT model FC102 drives
been outstanding. So we would embark on another
that delivered 100 hp at 460 V and provided a true
phase. As it stands now, we've installed more than
150 VLT drives, with more to come."
Above. Energy savings from the Danfoss drives is helping give the building
a greener reputation. Seventeen of the floors have qualified for Silver LEED
certification and six for Gold.
According to Sechler, the soft start eliminated a
The 841-ft. U.S. Steel Tower, once known as
lot of wear and tear on the motors-and also saved
the USX Tower, provides more than 2.3-million
energy. "We're talking big motors to pump water to a
sq. ft. of leasable space in downtown Pittsburgh. It
300-gal. cushioning tank on the sixty-fourth floor.
is the city's tallest skyscraper and the highest com-
From there, gravity feeds the water down fountains,
mercial building between Chicago and Philadel-
sinks, and toilets on the floors below. Only two of the
phia-with major tenants including U.S. Steel and
four pumps run at any given time in a lead-lag se-
the Univ. of Pittsburgh's Medical Center (UPMC),
quence that alternates weekly. But the old motor
speed controls were obsolete and parts were no longer
available. I don't have a record of energy savings from
that time. But I do know with the soft start on VLT
drives, pump motor rebuilds have been zero."
The next retrofit opportunity presented itself after
the state of Pennsylvania passed legislation in 2008
requiring Electric Distribution Companies (EDCs)
to reduce electricity consumption and peak demand.
(duquesnelight.com), provided a rebate program for
businesses that install variable-frequency drives to replace old-style motor speed-throttling technology.
"We jumped on this program," said Sechler. "We
knew what VLT drives did for our house water pumps.
So in 2010, we looked at what they could do for our
large 200- to 250-hp fan motors. These fans circulate
conditioned air in large office areas at a given static
pressure to satisfy the temperature setpoint. We ended up applying about 40 more FC102 drives for motors ranging from 30 hp to 250 hp.
"We were absolutely delighted with the energy
Built in 1970, the U.S. Steel Corp. headquarters stands 64 stories above the Pittsburgh skyline. While ahead of its time, the mechanical equipment was installed when
kilowatts cost pennies and oil was $3 a barrel. A series of retrofits using Danfoss VLT variable-frequency drives cut energy costs by more than $1 million.
COMMERCI A L A RCHI T EC T URE
savings, because the drives cut electricity costs by
$535,000 annually. And, along with those savings, we
got rebates that produced a one-year payback. So nat-